Gingivitis is a reversible infectious disease of the periodontia characterized by an inflamed periodontia that bleeds readily. Periodontitis is an infectious, destructive inflammatory disease of the soft and hard tissues surrounding the teeth and is the leading cause of edentulism. Moderate periodontitis occurs in a majority of adults, while the prevalence of severe, generalized disease is in the region of 10%.1 Increasing evidence suggests that periodontitis may be associated with increased risk of vascular diseases (including coronary artery disease and stroke), diabetes mellitus, lung diseases (COPD and pneumonia), and pre-term delivery.2-4 
Periodontitis is currently diagnosed on gross clinical manifestations, i.e. signs of gingival inflammation (e.g. redness, swelling), periodontal pocketing, and periodontal attachment or alveolar bone loss.5 Such manifestations are measured by periodontal probing and radiographs. Alveolar bone and periodontal attachment loss represent the results of the destructive aspects of host defense mechanisms responding to the microbial plaque biofilm present in the gingival sulcus, as well as the direct effects of virulence factors of periodontal pathogens. Longitudinal studies have indicated that progression of chronic periodontitis, in terms of loss of periodontal attachment, is infrequent and episodic, and most progression occurs in a smaller proportion of highly susceptible individuals.1,6 Furthermore, traditionally used diagnostic procedures (clinical signs) do not distinguish between disease-active and disease-inactive sites. In other words, without long-term longitudinal assessment, it cannot be determined if periodontal destruction is current or a reflection of past disease.5,7 Unfortunately tools for such longitudinal studies are not available. Thus, major diagnostic and prognostic problems exist for periodontitis.
Potential diagnostic tests that have been studied include: (a) the presence of specific bacteria (including Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans),8,9 or (b) their products (e.g. volatile sulfur compounds and proteolytic enzymes),10,11 (c) biomarkers which are involved in the disease process but produced by the host (e.g. matrix metalloproteinase-8,12 neutrophil elastase; aspartate aminotransferase; glucuronidase; and alkaline phosphatase,13 (d) biomarkers that occur as a consequence of tissue damage (e.g. collagen fragments),14 and (e) other markers of the inflammatory process e.g. subgingival temperature probes; prostaglandin E2; and interleukin-1.13-15 
To date, however, the predictive value of all potential markers has not been high enough for routine use in clinical practice. In addition, most diagnostic methods that have been investigated are too complicated for routine chair-side use. Furthermore, due to the complex nature of periodontitis—which involves a multifaceted immune and inflammatory reaction to a polymicrobial flora—a composite analytical approach to tissue and/or gingival crevicular fluid analysis is much more likely to prove successful than analysis of one or, at best, a few individual biomolecules.
If diagnosis using spectroscopy is viable, it would be widely applicable in dentistry. In general, spectroscopy is an attractive technology to apply to the study of periodontal inflammation and periodontal diseases as spectra can be captured instantly, no consumables need be purchased or developed (such as antibodies, substrates, or molecular probes), and, once the equipment is in place, it is very inexpensive to operate. Furthermore, commercially available portable spectrometers are small, they do not require cryogenic cooling, and therefore, can be readily utilized in small clinical environments, such as a periodontal operatory, and require minimal training to obtain reliable and reproducible data. Additionally, it is an entirely non-invasive technique that uses low energy radiation. Future studies are warranted that will establish the spectra that are characteristic of healthy and diseased periodontal sites in individual subjects with gingivitis and/or periodontitis.
Furthermore, the successful application of NIR spectroscopy to the study of periodontitis could provide great potential research benefits. It is generally accepted that the accuracy, reproducibility, and validity of the clinical index reporting are sensitive to subjective components.32 Indeed, Rosin et al.32 point out that non-invasive inflammatory indices (redness and edema) are even more susceptible to the negative influence of subjectivity than invasive measures. Thus, we propose that spectroscopy could conceivably represent a means of standardization of clinical measures of inflammation in periodontal tissues. Such standardized methods would have obvious benefits to both clinical studies and mechanistic studies.
EP 0 049 905 to Schief teaches a device for measuring gingival color intended especially for assessing gingival diseases. It provides that the light of a light source is fed via an optical fiber to a probe and illuminates the gingival tissue at the outlet. Via a second returning optical fiber, the reflected light is evaluated in a plurality of wavelength regions by means of filters, and fed to photoelectric components. The signals are then evaluated in an electronic device. It is not explicitly stated in the Schief patent which wavelength bands are examined, but it appears that the filters are chosen to detect blood flow with the measurement of deoxyhemoglobin and oxyhemoglobin.
U.S. Pat. No. 5,570,182 to Nathel et al. teaches the assessment of gingivitis by non-ionizing radiation. Specifically, Nathel et al. teach the mapping of a periodontal pocket to determine an attachment level of a tooth as well as alveolar bone level. Nathel et al. also teach absorption spectral analysis of teeth to distinguish active or inactive cavities from healthy teeth.
Several absorption bands in the visible and near infrared (NIR) spectral region reflect key inflammatory events.16,17 For instance, tissue edema—an index that is commonly used as a marker of gingival inflammation16,19—can be measured using MR spectroscopy.16,17 Thus, monitoring the intensity of the water bands in gingival tissues is expected to provide an index of tissue hydration representing a simple indicator of inflammation at specific periodontal sites.
In addition to measuring tissue water intensity, spectroscopy offers a non-invasive means of assessing the balance between tissue oxygen delivery and oxygen utilization. Hemoglobin and oxygenation indices have been previously measured in periodontal tissues with the data suggesting that the increase in blood supply during inflammation is insufficient to meet the oxygen demand in inflamed gingivae.21 The electronic transitions stemming from the heme ring and central metal ion of hemoglobin are particularly strong in the visible region. Spectroscopy can measure relative concentrations of oxygenated hemoglobin (HbO2) and deoxygenated (Hb) hemoglobin by fitting optical attenuation spectra to the known optical properties (extinction coefficients) of HbO2 and Hb.17,22 Thus, spectroscopy provides a measure of the hemoglobin oxygen saturation of tissues and the degree of tissue perfusion.
Increased hemoglobin levels are indicative of an increased blood perfusion, which, if severe enough, is clinically reflected in bleeding on probing. We have been able to use NIRS to show increased tissue perfusion in diseased tissues by monitoring hemoglobin dynamics. Thus, due to the strong signatures of hemoglobin molecules in the MR spectrum, NIRS provides a reliable indicator of both clinically-evident and sub-clinical tissue perfusion. We have also been able to use NIRS to show that oxygen saturation is significantly decreased in diseased periodontal tissues.
Tissue hypoxia occurs because of increased oxygen consumption by host cells during inflammatory reactions. Interestingly, it has been shown previously that tissue oxygen saturation correlates well with oxygen tension in periodontal pockets21 and the progression of inflammatory disease is known to be dependent upon infection with a complex microflora whose climax community is dominated by Gram negative anaerobic bacteria. Tissue oxygen saturation is not currently measured clinically, NIRS can provide a further index of inflammation that may prove useful to the periodontist. This suggests that spectroscopy has the potential to diagnose and assess inflammatory periodontal diseases.
Furthermore, the 960 nm water band is known to shift with tissue temperature and changes in electrolyte concentration.20 
Given the inadequacies of current techniques, there is a need for the development of a non-invasive technique for diagnosing periodontitis and other inflammatory diseases of the peridontia. Particularly desirable are diagnostic and prognostic tests having the following features:    1—simplicity and user friendliness which leads to easy training and reliable test results (low variability of results in dependence upon the tester),    2—low consumable, reagent-free application for minimizing costs associated with storage, spoilage, etc.,    3—chair-side applicability with equipment that is not massive, inordinately expensive, complex, susceptible to damage or malfunction, excessively sensitive to operating conditions, etc., and    4—targeted for site-specific diagnosis as opposed to a systemic test.